The present invention relates to an endoscope system capable of capturing in vivo normal light images and fluorescent light images of a surface of an object, and OCT (optical coherence tomography) images of the object.
Endoscope systems used for observing inside a body cavity of a patient have been conventionally known. An example of conventional endoscope systems includes an endoscope to be inserted in the body cavity of the patient, and an external device connected to the endoscope. The external device includes a light source and an image processor.
The endoscope includes an illuminating optical system, which is connected to:
the light source of the external device, the illuminating optical system emitting light toward an object to be observed for illuminating the same;
an objective optical system for forming an object image; and
a CCD (Charge Coupled Device), which is arranged at an image plane of the objective optical system and is connected to the image processor of the external device.
At the distal end of the endoscope, an instrument outlet, from which various treatment instruments such as a forceps are to be protruded, is defined.
An operator of the endoscope system inserts the endoscope inside the body cavity of the patient, and illuminates paries of the cavity with the light emitted through the illuminating optical system. An image of the paries is formed by an objective optical system. The CCD converts the thus formed image (optical image) into an electrical signal (i.e., electrical image) and transmits the signal to the image processor included in the external device.
The external device processes the received image signal representing the image of the paries of the body cavity, and displays the image on a monitor. Thus, the operator is capable of observing the image of the paries of the body cavity displayed on the monitor.
If the operator determines that there is a portion which might be cancered or tumorous, the operator collects the biotissues at the portion using forceps or a biopsy needle protruded from the instrument outlet. The thus obtained biotissues are subjected to a pathological examination, based on the results of which a diagnosis is made.
In the conventional endoscope as described above, the displayed image shows only the surface of the paries of the body cavity. In order to know the condition of the tissues beneath the surface of the paries, biopsy is required. In particular, in order to detect cancer in its earliest form or relatively small tumors, the biopsy is indispensable. However, pathologic investigation of the biotissues obtained by the biopsy generally takes time, and therefore, the diagnosis also takes time.
Further, in view of the burden to the patient, the biopsy is to be done for only a limited portion by a limited amount of time. However, there is a possibility that portions other than those identified by the operator are diseased. Thus, unless the biopsy is done with respect to the diseased area, the accurate diagnosis cannot be expected.
Incidentally, a method for obtaining tomogram of biotissues utilizing a combination of a low-coherent light source such as a superluminescent diode (SLD) and a Michelson interferometer has been developed. Such a method is known as an OCT (Optical Coherent Tomography) system, an example of which is described in U.S. Pat. No. 5,321,501, the teachings of which are incorporated herein by reference.
For one solution of the afore-mentioned problem, an imaging system including a probe of the OCT has been known. Such a system is described in xe2x80x9cIn vivo endoscopic OCT imaging of precancer and cancer states of human mucosaxe2x80x9d, by A. M. Sergeev et al., Dec. 22, 1997, vol. 1, No. 13 of OPTICS EXPRESS pp. 432-440, teaching of which is incorporated herein by reference.
In the above OCT system, however, a tomogram for a relatively wide area cannot be obtained at one time. Therefore, an operator of the system designates a portion, which might be diseased, and the OCT imaging is performed with respect to the designated portion. If the OCT system is incorporated in an endoscope system, the operator inserts the endoscope in the body cavity for normal observation, identifies a portion which might be diseased, and then performs the OCT imaging with respect to the identified portion.
FIG. 6 shows an example of a conventional OCT imaging system for an endoscope. In FIG. 6, a distal end portion 7 of the endoscope is shown. The distal end portion 7 has a substantially cylindrical shape, and on the tip end surface, an illumination window 71, an observation window 72 and an instrument outlet opening 73 are formed. Inside the endoscope, although not shown, an illuminating optical system for directing a visible light beam is provided. Further, the endoscope is provided with an objective optical system (not shown) for receiving light from an object (e.g., a surface of the paries which is considered to be diseased) and forming an object image on an image receiving surface of a CCD (Charge Coupled Device), not shown.
The illumination optical system emits visible light through the illumination window 71 toward the object. The light reflected by the object enters the objective lens system through the observation window 72. Then, an image of the object is formed on the image receiving surface of the CCD. The CCD then outputs an image signal, which is processed and displayed on a monitor 8 as a normal image.
Separate from the endoscope, an OCT apparatus having the SLD and a Michelson interferometer is provided. The interferometer Is provided with a measuring optical system and a reference optical system. The measuring optical system includes a fiber probe 9, which is inserted through the endoscope, and the tip thereof is protruded from the instrument outlet 73 of the distal end portion 7 of the endoscope. The OCT apparatus is also connected to the monitor 8, and an OCT image of a portion facing the tip end of the fiber probe 9 is displayed on the monitor 8.
When in use, the operator inserts the endoscope inside the body cavity of the patient, and observes the normal image of the paries. If a portion which might be diseased is found, the operator makes the fiber probe 9 protrude from the instrument outlet 73 to confront with the portion in question. Then, the OCT apparatus is operated to capture a tomogram of the portion in question, and displays the same on the monitor 8.
The monitor 8 is capable of selectively displaying the normal image and the OCT image in accordance with operation of switches and/or keyboard 6. In FIG. 6, the monitor 8 displaying the normal image and the monitor 8 displaying the OCT image are drawn in order to show both conditions. Actually, however, the endoscope system is provided with only one monitor 8, and one of the normal image and the OCT image is displayed on the monitor 8. The operator makes diagnosis in accordance with thus displayed images.
According to the conventional endoscope system described above, the fiber probe 9 of the OCT apparatus protrudes from the instrument outlet 73. The fiber probe 9 is located within a field of view of the objective optical system. Therefore, in the normal image displayed on the monitor 8, the fiber probe 9 appears and forms a dead angle. The dead angle disturbs the observation of the normal image, which prevents the operator from recognizing positional relationship between the normal image and the OCT image.
In order to avoid such a problem, the objective optical system for the normal image and the tip of the measuring optical system of the OCT apparatus can be Integrated to a single optical system. In such a case, however, it becomes generally necessary to split optical paths of the normal image and the OCT image utilizing a half mirror, a dichroic mirror and the like. In such a configuration, the light amount is decreased when the light incident from the object is split, which deteriorates quality of the images.
In view of the above problems, it is an object of the present invention to provide an improved endoscope system that enables diagnosis accurately within a relatively short period of time.
Another object of the present invention is to provide an improved endoscope system which is capable of capturing images of relatively high quality, and is also capable of obtaining the OCT image.
For an object, according to the present invention, there is provided an endoscope system, which is provided with an illuminating optical system that emits at least one of visible light and excitation light for illuminating an object to be observed, the excitation light causing biotissues to fluoresce, an objective optical system that converges light from the object to form an optical image of the object, an image capturing system that captures the optical image formed by the objective optical system, a first light guide, a second light guide, a coupler, the first and second light guides being optically coupled by the coupler, a low-coherent light source arranged on a proximal end side of one of the first and second light guides, a low-coherent light beam emitted by the low-coherent light source being incident on the one of the first and second light guides, a scanning unit that causes the low-coherent light beam emerged from a tip of the first light guide to scan on the object, the low-coherent light reflected by the object being directed to the first light guide by the scanning unit as detecting light, a mirror that reflects the low-coherent light beam emerged from a tip of the second light guide so as to impinges on the tip of the second light guide as reference light, an optical path length adjusting system that changes a length of an optical path from the coupler to the object via the first light guide relative to a length of an optical path from the coupler to the mirror via the second light guide, a detector arranged on a proximal end side of the other of the first and second light guides, the detector detecting interference fringe generated by interference between the detecting light and the reference light and outputs an electrical signal, and a signal processing system that captures a tomogram of the object based on the signal that is output by the detector when the optical path length adjusting system and the scanning unit operate.
As above, the OCT image can be observed by monitoring the normal light image or the fluorescent light image. Therefore, diagnosis can be accurately performed within a relatively short period of time.
Optionally, the optical path length adjusting system may be configured to vary the length of the optical path from the coupler to the object via the first light guide relative to the length of the optical path from the coupler to the mirror via the second light guide by moving the mirror in a direction parallel to the central axis of the tip of the second light guide.
Further optionally, the signal processing system forms the tomogram of the object based on the signal output by the detector when the optical path length adjusting system periodically varies the length of the optical path from the coupler to the object via the first light guide relative to the length of the optical path from the coupler to the mirror via the second light guide, and when the scanning unit operates.
In particular, the signal processing system forms the tomogram when the optical path length adjusting system sequentially varies the length of the optical path from the coupler to the object via the first light guide relative to the length of the optical path from the coupler to the mirror via the second light guide for each scanning position.
Further optionally, the endoscope system may be provided with a visible light source, an excitation light source, a light source switching system that selectively introduces the light emitted by the visible light source and the excitation light source to the illuminating optical system. In this case, the objective optical system may form a normal light image of the object when the visible light is introduced to the illuminating, optical system, and the objective optical system may form a fluorescent light image of the object when the excitation light is introduced to the illuminating optical system.
Preferably, the low-coherent light source includes a superluminescent diode.
Still optionally, the endoscope system may include a display system for displaying an image of the surface of the object captured by the image capturing system and the tomogram of the object obtained by the signal processing system.
Further optionally, the scanning system emits the scanning beam through a scanning window, the scanning window being formed on an insertion tube of an endoscope of the endoscope system, the scanning window being located out of field of view of the objective optical system, the scanning window facing the object that is located within the field of view of the objective optical system.
With this structure, observation of the normal light image and/or fluorescent light image may not be disturbed by the tip portion of the insertion tube of the endoscope.
Optionally, the insertion tube includes a cylindrical portion and a flatter portion formed at a tip of the cylindrical portion, an inclined surface connecting side surfaces of the cylindrical portion and the flatter portion. Further, the illuminating optical system includes an illuminating lens that is fixed on the inclined surface and emits light toward the object. The objective optical system includes an objective lens that is fixed on the inclined surface and receives the light from the object, and the scanning window is provided on the side surface of the flatter portion.
Further optionally, the optical path length adjusting system may vary the length of the optical path from the coupler to the object via the first light guide relative to the length of the optical path from the coupler to the mirror via the second light guide by moving the mirror in a direction parallel to the central axis of the tip of the second light guide.
Further, the endoscope system may further be provided with a visible light source, an excitation light source, a light source switching system that selectively introduces the light emitted by the visible light source and the excitation light source to the illuminating optical system. In this case, the objective optical system forms a normal light image of the object when the visible light is introduced to the illuminating optical system, and the objective optical system forms a fluorescent light image of the object when the excitation light is introduced to the illuminating optical system.
Still optionally, the endoscope system may further be provided with a display system for displaying an image of the surface of the object captured by the image capturing system and the tomogram of the object obtained by the signal processing system.